function y = e_t(x)
% Extended Trigonometric function
%x0=[0.2, 0.2, ....,0.2]
%fmin=n/2
%Author:shi yangyang
n=length(x);
y=ones(1,n);
s=n;
for i=1:1:n
    s=s-cos(x(i));
end
for i=1:1:n
    y(i)=(s+i*(1-cos(x(i)))-sin(x(i)))^2;
end
y=sum(y);
